Allotropy is defined as the occurrence of an element in two or more crystalline forms. This concept is analogous to isomerism which refers to compounds with the same molecular formula, but different chemical and physical properties. Dimethyl ether and ethyl alcohol, for example, both have the formula C₂H ₆O, but the two compounds have quite different properties.

In 1830, Jöns Berzelius raised the question as to whether elements might exhibit a similar phenomenon, that is, whether any given element might exist in two or more forms with different chemical and physical properties. A decade later he suggested the name allotropy--Greek for " another manner"--for such a phenomenon. Berzelius already knew of elements with this property-- carbon, phosphorus, and sulfur in particular. But he did no further research on the subject.

Other chemists tried to apply the concept of allotropy to elements that puzzled them. For...